Bernd Riedstra

Early feather pecking as a form of social exploration: the effect of group stability on feather pecking and tonic immobility in domestic chicks

Abstract In two lines of White Leghorns that differ in their propensity to feather peck, feather pecking was already present 1 day after hatching. A significant line difference developed within 3 days and this difference remained in the following weeks. There was no clear relationship between feather pecking and ground pecking, instead feather pecking was associated with other socially orientated pecks. When chicks were confronted with feathers as an inanimate stimulus pecking at these feathers did not reflect pecking in a social context. These results suggest that feather pecking has an underlying social component, rather than being a redirected behaviour. To test the influence of social factors on feather pecking, chicks from the high feather pecking line were subjected to regular rehousing or regular rehousing plus confrontation with unfamiliar peers. Gentle feather pecking increased significantly in groups that were rehoused with unfamiliar peers. Directly after confrontation chicks displayed a preference in the total number of pecks toward these unfamiliar birds. Gentle feather pecking as a separate pecking orientation showed a similar trend. Increased righting times in a tonic immobility test were recorded in the experimental groups, hence frequent confrontation with unfamiliar peers may be experienced by chicks as stressful, which is consistent with the hypothesis that stress mediates the expression of feather pecking. In contrast to the dominant hypotheses in the field, we argue that gentle feather pecking at an early age plays an important role in the building (social exploration) and maintenance of social relationships between chicks.

The prevention and control of feather pecking in laying hens: identifying the underlying principles

Feather pecking (FP) in laying hens remains an important economic and welfare issue. This paper reviews the literature on causes of FP in laying hens. With the ban on conventional cages in the EU from 2012 and the expected future ban on beak trimming in many European countries, addressing this welfare issue has become more pressing than ever. The aim of this review paper is to provide a detailed overview of underlying principles of FP. FP is affected by many different factors and any approach to prevent or reduce FP in commercial flocks should acknowledge that fact and use a multifactorial approach to address this issue. Two forms of FP can be distinguished: gentle FP and severe FP. Severe FP causes the most welfare issues in commercial flocks. Severe FP is clearly related to feeding and foraging behaviour and its development seems to be enhanced in conditions where birds have difficulty in coping with environmental stressors. Stimulating feeding and foraging behaviour by providing high-fibre diets and suitable litter from an early age onwards, and controlling fear and stress levels through genetic selection, reducing maternal stress and improving the stockmanship skills of the farmer, together offer the best prospect for preventing or controlling FP.

DAILY ENERGY EXPENDITURE OF MALE AND FEMALE MARSH HARRIER NESTLINGS

We used the doubly labeled water (DLW) method to measure daily energy expenditure (DEE) in eight brother-sister pairs of free-living Marsh Harrier (Circus aerugi- nosus) nestlings. We calculated metabolizable energy intake (ME) from DEE and body-mass change. In each pair, males had lower body mass, DEE, and ME than their female siblings. On average, male body mass was 20%, DEE 19%, and ME 20% lower than that of female siblings. Thus, energy turnover was proportional to body mass. Because the average sex ratio at fledging in Marsh Harriers is 55% male, and the energy requirement of sons is 45% of the son-daughter pair, this sex ratio matches exactly that predicted by Fishers theory (1930). A literature review revealed that DEE (kJ/ day) measured by DLW when nestlings were ap- proximately 95% of asymptotic or fledging mass scaled as 4.58 M 0-76 (where M = body mass in g) in 11 species of altricial nestlings, including the Marsh Harrier. Received 14 November 1996, accepted 3 December 1997.

Examining a pathway for hormone mediated maternal effects--yolk testosterone affects androgen receptor expression and endogenous testosterone production in young chicks (Gallus gallus domesticus).

In vertebrates maternal androgens can substantially influence developing offspring, inducing both short and long term changes in physiology and behavior, including androgen sensitive traits. However, how the effects of maternal hormones are mediated remains unknown. Two possible pathways are that maternal androgens affect parts of the hypothalamus-pituitary-gonadal axis (HPG axis) or the sensitivity to androgens by affecting androgen receptor (AR) densities within the brain. To investigate both pathways, testosterone within the physiological range or vehicle only was injected into the egg yolk of unincubated chicken eggs and AR mRNA expression in different brain nuclei as well as plasma testosterone levels were measured in two week old male and female chicks that had hatched from these eggs. Our results showed a significant sex difference in plasma testosterone levels with males showing higher levels than females. Furthermore, AR mRNA expression as well as plasma testosterone levels were significantly lower in chicks hatched from testosterone treated eggs. These results suggest a compensatory mechanism for avoiding potential detrimental effects of high testosterone levels.

Increased exposure to yolk testosterone has feminizing effects in chickens, Gallus gallus domesticus

Competing for food by altricial and semiprecocial bird nestlings is a behaviour well known for its sensitivity to maternal androgens during prenatal development. Whether a similar effect is present in precocial species that do not beg is less well known. We therefore increased yolk testosterone levels within the physiological range at the onset of incubation to study its effects on food competition behaviour in the domestic chicken, Gallus gallus domesticus. We found an increase in competitiveness in testosterone-treated male domestic chicks, raising their level to that of the females. This is in line with the decrease in circulating plasma levels of males in the direction of the levels in females, and the overall decrease in androgen receptor densities after prenatal treatment as found previously. Hormones are known to have long-lasting organizing effects on behaviour and to affect sexual differentiation in vertebrates. Although research into hormone-mediated maternal effects has been productive, only a few studies describe (the ambiguous) effects into adulthood. Therefore we followed our animals into adulthood and recorded androgen-dependent social behaviour and secondary sexual characteristics, body mass and circulating plasma testosterone levels and checked whether these variables were treatment dependent. Treatment had a near significant effect on comb colour (both brightness and chroma). Again treatment caused a shift towards a more female-like phenotype. This suggests that, in contrast to earlier suggestions, maternal androgens may interact with (but not disrupt) sexual differentiation of brain and behaviour and the development of secondary sexual characteristics

Organisational and Activational Effects of Prenatal Exposure to Testosterone on Lateralisation in the Domestic Chicken ( Gallus gallus domesticus )

Brain lateralisation is the specialisation of the two hemispheres on different tasks and is supposedly beneficial for individuals. There is a long-standing debate about to what extent and via which pathways prenatal exposure to testosterone affects lateralisation. Birds are excellent models to investigate this since the embryo can be manipulated outside the mother’s body. Moreover, avian eggs contain substantial concentrations of maternally derived hormones known to affect a wide array of behaviours. Therefore, birds provide an excellent model to integrate two flourishing fields: that of hormone mediated maternal effects and of lateralisation. In addition, in most birds the eyes are placed laterally and the information exchange between the two hemispheres is limited, facilitating measuring lateralisation of visually guided behaviour. We will discuss results of egg injection experiments on short- and long-term effects on the lateralisation of visually guided behaviours in the domestic chicken. Lateralisation in young birds, young chicken in particular, has been extensively studied, but to what extent lateralisation is consistent over life and affected by prenatal exposure in adult birds remains elusive. Our results do not show an effect of the prenatal manipulation, in contrast to some other studies, perhaps because ours were carefully carried out within the physiological range of the species. They therefore do not lend support for either of the three main hypotheses about how prenatal testosterone affects the development of lateralisation in the ‘Geschwind-Behan–Galaburda’ hypothesis, the ‘Corpus Callosum’ hypothesis and the ‘sexual differentiation’ hypothesis. Correlations between testosterone levels and lateralisation both measured in adulthood suggest a role for activating effects of this hormone on lateralisation, at least in males. Correlations of lateralisation indices at young and adult age within individuals were also inconsistent, suggesting brain reorganisation during late development and challenging functional explanations of lateralisation for adult chickens.